When printing with a laser printer, once the printer starts to move the paper, it cannot stop. Therefore, the image rendering computer in the laser printer must provide the raster information as fast as the laser needs the information to keep-up with the paper. This may pose a problem when a printer must print a complex page such as one containing Asian characters. With present technology of laser printers, all of the unique characters to be printed for a given page are rendered and placed into a "font cache." Also, before a page is committed to the laser, all of the characters used in the following page are cached. As the page is exposed, the characters are pulled out of the cache and then placed in the proper place in memory. This requires sufficient memory for a font cache to store each unique character.
The maximum number of characters on an A3 page can approach 5000. Not all these characters are unique. With many languages, the number of unique characters may actually be relatively small, somewhere on the order of 50 to 100. However with some languages such as Japanese Kanji, which includes Katakana and Hirafiana, it is estimated that a font cache of 1800-2000 characters is required to obtain a "reasonable" font cache hit rate. Also, Chinese characters, and other Asian characters could include over 2000 unique characters. Other languages such as Arabic may also have a high number of unique characters.
The amount of space consumed by a 12 point, 600 dpi character is approximately 1600 bytes. Therefore, a font cache of 3.2 megabyte (2000 characters) is required to support printing an A3 page in the Asian market.
An alternative approach to this problem is to render the characters as the page is being exposed. This is commonly called "racing the laser." This typically requires a new method to render the characters as present formatters render between 6 and 40 Asian characters per second. These numbers are expected to only double with the next generation formatters. To obtain significant improvements usually implies a hardware solution for rendering characters. However, even hardware solutions may not have the bandwidth to process the worst case page. The problem comes in trying to process a "strip" of a page that has too many characters. Such a strip will be overrun by the laser.
Therefore the primary purpose of the present invention is to provide a method that brings the elements of a partial font cache, and a high speed rendering process together to print complex Asian pages quickly with reduced memory requirements.